Ozone concentration in ozonated water is often measured via absorption spectroscopy. Ultraviolet (UV) and yellow-red bands of light are suitable due to a good match to ozone's absorption characteristics. The peak absorption for the UV Hartley band is about 2000 times greater than for the yellow-red Chappius band, so use of a UV source can provide greater measurement sensitivity than use of a yellow-red source. A UV source, however, can be expensive and can produce an unstable light intensity. Therefore, use of visible light can be preferred when the greatest sensitivity is not required.
Ozonated water has many industrial applications. In the semiconductor manufacturing industry, for example, accurate control of the ozone concentration of ozonated water produced by an ozonated water generator can be critical during device fabrication. Common approaches to measuring ozone concentration for such generators are often slow, prone to error, and/or inconvenient. For example, ozone concentration can be measured by collecting a sample of ozonated water from the generator and testing it with an absorption spectroscopy-based analytical device. Thus, there can be errors and delays in measurements due to sample handling. Further errors can be introduced by anomalous scattering of light as it passes through the water. Such scattering caused, for example, by bubbles, can produce light intensity losses that can be difficult to distinguish from intensity losses that are due to ozone absorption.